Australian authorities say the exhaustive southern search mission for missing Malaysian Airlines flight MH370 has been given a significant boost by credible new leads in the remote Indian Ocean.

But the agency tasked with leading the search mission warned it was a 'challenging search operation' and that it 'continues to hold grave fears for the passengers and crew' on board the doomed Boeing 777-200, which mysteriously disappeared March 8.

A third large object spotted via a Chinese satellite and a civilian plane sighting of debris in the search zone, about 2,500 kilometres off the coast of Perth, were among 'three significant developments' in the search operation, according to Australian Prime Minister Tony Abbott.

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A photo released by Chinese broadcaster CCTV shows a satellite image of a large floating object in the Indian Ocean that could be related to missing Malaysia Airlines flight MH370

Squadron leader Brett McKenzie takes notes of other search aircraft on the windshield of a Royal New Zealand Air Force P-3K2 Orion aircraft searching for missing Malaysian Airlines flight MH370 over the southern Indian Ocean

Australian Prime Minister Tony Abbott says 'three significant developments' have offered 'increasing hope' of finding MH370, as the search continues in the southern Indian Ocean

Speaking from Papau New Guinea, Mr Abbott said the search effort spearheaded by the Australian Maritime Safety Authority (AMSA) said there was 'increasing hope' of finding wreckage of doomed flight MH370, but warned it was 'no more than hope'.

'Over the last 24 hours there have been three significant developments,' he said.

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'New Chinese satellite imagery does seem to suggest at least one large object down there, consistent with the object that earlier satellite imagery discovered which I told the Australian Parliament about last week.

'Yesterday one of our civilian search aircraft got visuals on a number of objects in a fairly small area in the overall Australian search zone.

'Obviously we have now had a number of very credible leads and there is increasing hope, no more than hope, that we might be on the road to discovering what did happen.'

A relative of Chinese passengers aboard the missing Malaysia Airlines, MH370, expresses her frustration at the lack of information, to journalists in Beijing

Working: Leading Seaman Luke Horsburgh stands watch during his duty as Quartermaster on the bridge of the Australian Navy ship HMAS Success after it arrived in the search area for missing MH370

Mr Abbott also reported that four new aircraft - two Chinese planes and two Japanese Orions - would join an expanding fleet of military and commercial planes, ships and helicopters scouring the search zone.

Chinese satellites Saturday picked up signs of a 'suspicious' object measuring 72ft by 42ft in an area 75 miles west of where Australia reported an earlier sighting of floating debris.

The Chinese satellite discovery was revealed this morning by Malaysia's acting Transport Minister Hishammuddin Hussein at a press conference where he gave the latest updates on the search for the missing airliner.

He made the announcement after being handed a handwritten note, adding that Chinese authorities would make an official announcement 'in a couple of hours'.

A new hope: Malaysian Transport Minister Hishammuddin Hussein holds up the note on which he was passed the information about the Chinese satellite sighting in the southern Indian Ocean

Hand-written: A close up of the note passed to Mr Hussein. It is understood that the '30m' figure is incorrect

Radar specialists are pictured aboard a Royal New Zealand Air Force P-3K2 Orion aircraft searching for missing Malaysian Airlines flight MH370 over the southern Indian Ocean

The images were taken at lunchtime on March 18, Chinese state media reported, just two days after the sighting by Australian satellites singled out the area in the southern Indian Ocean.

Since the announcement, Australian search teams scouring the remote area reported seeing a number of small objects including a wooden pallet. AMSA revealed Sunday that straps were also spotted in the water near the pallet.

A Royal New Zealand Air Force P3 Orion plane with specialist electro-optic observation equipment was diverted to the location, arriving after the first aircraft left but only reported sighting clumps of seaweed.

AMSA confirmed Sunday 'several small objects of interest' were spotted by a civil aircraft, but warned that difficult conditions may conspire against the search operation.

'The Australian Maritime Safety Authority (AMSA) reiterates this is a challenging search operation and continues to hold grave fears for the passengers and crew on board the missing flight,' AMSA announced in a release.

A graphic from the Australian Maritime Safety Authority (AMSA), shows the approximate position of the objects seen floating in a Chinese satellite image in the southern Indian Ocean, and the area where a civilian plane reported sighting possible debris

Reporting: Journalists wait for Chinese relatives of missing Malaysia Airlines flight MH370 outside the hall, during a meeting with airline officials at the Metro Park Lido Hotel in Beijing

The search for wreckage intensified Sunday with eight aircraft including four commercial planes splitting into two search squadrons over the target area, raising hopes of more sightings.

AMSA has dispatched two Bombardier Global Express planes, and a Gulfstream 5 and Airbus 319 took off before 9am Perth time.

The US Navy Poseidon and a RAAF Orion have also left on the search, and will be followed by a second Australian Orion late in the morning, and another from the New Zealand Air Force in the early afternoon.

AMSA said information gained by calculating likely tidal drift of the objects in the initial satellite images had determined today's search areas, which had narrowed to 59,000 square kilometres.

The two Chinese military aircraft, Russian-made Ilyushin IL-76 planes, which flew in on Saturday each with around 20 crew, will now not join the search until Monday.

'Today is a visual search again,' John Young, the general manager of AMSA's Emergency Response Division, said Sunday afternoon.

'Our plan is to continue seeking to make sightings from the visual search looking for the objects identified in the satellite imagery.

'Our focus is to define the very best search area. It is proving difficult to re-locate these items.'

AMSA described the search as taking a different approach from radar tracking, and said the search area would change depending on currents and further satellite information that may be forthcoming.

Flight Lieutenant Jason Nichols on board a Royal Australian Air Force AP-3C Orion, takes notes as they search for debris from missing Malaysian Airlines flight MH370 earlier today in the southern Indian Ocean

RAAF Flight officer Rayan Gharazeddine looks out from an Orion as he scans for signs of debris or wreckage

A Japan Maritime Self-Defence Force personnel looks out of their Lockheed P-3C Orion aircrafts before leaving for Australia to help with the search operations for MH370

Mr Hishammuddin's announcement came after the first Australian Orion aircraft to make a sortie over the target zone
for missing Flight MH370 returned without success.

Flying
Officer Peter Moore, the aircraft's captain, said a combination of
'less than ideal' weather and sea conditions had closed in on the
flight.

He said his crew
had flown through 'a thick layer of cloud from 2000 feet to 500 feet,
isolate showers and sea fog above the surface'.

However,
the aircraft had managed to cover 100 per cent of its planned search
area, with RAAF officers manning the visual observer station on board.

'However, we weren't able to find any evidence of wreckage from the missing Malaysian aircraft,' officer Moore said.

Since Australia announced the first image of what could be parts of the aircraft on Thursday, the international search for the plane has focused on an expanse of ocean more than 2,000 km (1,200 miles) southwest of Perth.

AMSA said one of its aircraft reported sighting a number of 'small objects' with the naked eye, including a wooden pallet, within a radius of five km.

The RNZAF P-3 Orion aircraft sent to take a closer look only reported seeing clumps of seaweed. It dropped a marker buoy to track the movement.

'A merchant ship in the area has been tasked to relocate and seek to identify the material,' AMSA said in a statement.

Flying Officer Peter Moore, the aircraft's captain, said a combination of 'less than ideal' weather and sea conditions had closed in on the flight

Two Chinese Ilyushin IL-76s aircraft sit on the tarmac at RAAF Pearce base ready to join the search missing Malaysia Airlines flight MH370 in the southern Indian Ocean

The latest developments came after Australia's acting prime minister said the air and sea search for missing Malaysian Airlines
flight MH370 'will continue while there's still hope'.

Warren
Truss said no time limit had been placed on the operation which will
continue 'indefinitely' and 'until we are absolutely satisfied further
searching is futile.'

He
spoke at RAAF airbase Pearce in Perth, western Australia, after meeting
with sailors and airmen who have been scouring a remote area of the
southern Indian Ocean where debris was spotted by satellite six days
ago.

Australia, which announced the potential find and is coordinating the rescue, has cautioned the objects might be a lost shipping container or other debris and may have since sunk.

Searches by more than two dozen countries have so far turned up little but frustration and fresh questions about the passenger jet which disappeared on a scheduled flight from Kuala Lumpur to Beijing on March 8.

AMSA confirmed Sunday that merchant ship Hoegh ST Petersburg had been released from the search party.

The Norwegian vessel had been the first ship to reach the target zone after AMSA and the Australian Defence Force dispatched a team Thursday.

Acting Prime Minister of Australia Warren Truss speaks to the media at the RAAF Pearce Base, where he said the search for MH370 would continue 'while there's still hope' and until officials were certain it was 'futile'

Mr Truss walks with RAAF Wing Commander James Parton and RAAF Group Captain Craig Heap: Mr Truss dismissed a suggestion the Australian Government had waited too long to act after revealing the satellite photos

Asked whether there were any other satellite images yet to be released, Mr Truss said the Australia was 'not seeking to withold information'.

'If there is new imagery that is relevant and can be released to the media, it will be,' he said.

'We know the families are anxious for information.'

Mr Truss and the operation's commander, Group Captain Craig Heap, said identifying and locating the two objects captured on satellite imagea would most likely be done qitwh the naked eye.

'It is primarily a visual search,' Mr Truss said. 'You need to be low, you need to be close.'

Captain Heap added: 'It's a very difficult search, but if there's something out there and we are on top of the area will find [it].'

Uncertainty: A Chinese woman who is a relative of a passenger carries her three-year-old daughter as she arrives at Metro Park Lido Hotel in Beijing

Speaking on the edge of the air base tarmac as the sixth search plane of the day prepared to take off for the remote Indian ocean, Mr Truss said the arrival of two Chinese planes today and a Japanese aircraft tomorrow, as well as Chinese naval boats soon was a huge boost to the operation.

'This search is intensive, ' he said.

'We have had 15 sorties so far and no findings, but we are searching new areas because of the drift that has occurred.

'With the arrival of the Chinese fleet, with refuelling [support], it has the capability to stay in the area for a long time.'

Mr Truss dismissed a suggestion the Australian Government had waited too long to act following the discovery of the satellite images, risking the debris sinking to the ocean floor.

He said the search had been launched at the earliest possible moment 'in relation to the time of the imagery was created' and 'as soon as they were identified' the government had acted.

He defended Tony Abbott's perceived backdown from insisting the debris was MH370, to conceding a day later it could be a shipping container.

'There's a lot of debris floating around the globe continuously and containers fall off ships,' he said.

'But even if it's not a definite lead, it is a more solid lead than any other.'

Mr Truss said Australia had the capability to co-ordinate a large international flotilla and aircraft from all over the world, as more countries sent craft and crew to Perth.

Mr Hussein, Malaysia's defence minister, said yesterday searchers realised that time was running out. The 'black box' voice and data recorder only transmits an electronic signal for about 30 days before its battery dies.

Difficult time: Relatives of passengers of the missing Malaysia Airlines flight MH370 are seen coming out of a conference room wearing t-shirts reading 'Pray for MH370 Come Back Home Safely', at a hotel in Beijing

A RAAF AP-3C Orion aircraft from 92 Wing on the flight line at dusk at RAAF base Pearce in Perth, Western Australia, yesterday, after completing a search sortie for Flight MH370

Hopes are increasingly pinned on the search area identified by Australian satellite images six days ago after India told Malaysia it found no evidence that the missing jet flew through its airspace.

China and Pakistan are also among countries that have found no trace of the jet in their airspace, said Mr Hussein, Malaysia's acting transport minister.

The response from India is crucial because any radar data from that country could help identify whether the jet turned north or south after disappearing on March 8, but the issue is also sensitive because of the presence of military radar.

Sources familiar with the situation in both countries said India had formally told Malaysia that it had checked for any sign of the jet having touched its airspace and found nothing of significance, in response to Kuala Lumpur's diplomatic request.

The plane's last confirmed position, picked up by Malaysian military radar, was at 2.15am Malaysia time (1815 GMT March 7) about 200 nautical miles north-west of Malaysia's Penang island, roughly an hour after it diverted from its scheduled route from Kuala Lumpur to Beijing.

India has said it is possible that the military radars were switched off as it operates on an 'as required' basis in that area.

A reluctance to share sensitive military radar data in a region where countries are wary of each other has hampered investigators' attempts to solve the baffling disappearance, officials have said.

Investigators suspect the Boeing 777 was deliberately diverted thousands of miles from its scheduled path. They say they are focusing on hijacking or sabotage but have not ruled out technical problems.

The Daily Telegraph published what it said was a transcript of communications between the cockpit of Flight MH370 and Malaysian air control, but few if any new clues emerged.

A Royal Australia Air Force AP3C Orion leaves RAAF Pearce Air Base in search of MH370. The flight went missing more than two weeks ago carrying 239 passengers and crew on route from Kuala Lumpur to Beijing

The search itself has strained ties between China and Malaysia, with Beijing repeatedly leaning on the South East Asian nation to step up its hunt and do a better job at looking after the relatives of the Chinese passengers.

For families of the passengers, the process has proved to be an emotionally wrenching battle to elicit information.

In a statement today, relatives in Beijing lambasted a Malaysian delegation for 'concealing the truth' and 'making fools' out of the families after they said they left a meeting without answering all their questions.

'This kind of conduct neglects the lives of all the passengers, shows contempt for all their families, and even more, tramples on the dignity of Chinese people and the Chinese government,' they said.

Some experts have argued that the reluctance to share sensitive radar data and capabilities in a region fraught with suspicion amid China's military rise and territorial disputes may have hampered the search.